Television apparatus and method for phase-shift scanning



I E /0 A A 1 I i i 1 I I J YL /6. Z .J i ]F" INVENTOR ENG. Tau/on Dec. 23, 1952 P. M. G. TOULON 2,623,196

TELEVISION APPARATUS AND METHOD FOR PHASE-SHIFT SCANNING Filed Feb. 28, 1950 2 SHEETSSHEET 1 -BY 74 Aloe! ATTORNEYS Dec. 23, 1952 TQULON 2,623,196

TELEVISION APPARATUS AND METHOD FOR PHASE-SHIFT SCANNING Filed Feb. 28, 1950 2 SHEETSSHEET 2 /\9 '7 L 1L:1l/ 1/ L 1/ L 1/ 5 I z 4 I z i y zeo7 ze 0 INVENTOR P /7. G Tau/0n TELEVISIQON'APPARATUS AND METHOD FOR PHASE-SHIFT SCANNING V i t Pierre Marie Gabriel Toulon, New York, N.'Y.,

assignor to Products and Licensing Corporation, New York, Y., a corporation of Dela-.

. ware 1 The presentinvention relates to the control of the deviation of the electron beam in a cathode ray tube.

.Theimention applies particularly to television and is of especial value in colortelevision ap 'pa-ratus and systems. It ,i s 'we11 known that the exploration of all points of a a television screen surface can be .rnade.;in various ways. In the most simple process; all the points of each line are successively .and continuously explored. In another classical process, called line interlaced scanning the odd lines of; the first frame are explored sequentially and afterwards the even lines are explored in a second scanning; Inanother process, "dot in- .terlaced scanning, instead of scanning all suc- .cessive= points of each line, the cathode raybeam explores individual elemental areas or points in groups of six, nine, twelve or sixteen areas per group for each frame; and afterwards the other points of each group are reached in the course of successive scannings of the picture.

- The new control process of the electron beam according to the invention; is particularly useful to, the application of dot interlaced scanning. The deflectionof the cathode ray is usually obtained magnetically. or electrostatically by means of a sawtooth'generator. The frequency of such ;a generator. is synchronized by synchronizing signals, line-or'imag'e, sent generallyth'rough the samerch'annel, and separated from the video signals through itscharacteristics,- namely relative amplitude or sign. As the deviation of thecathode ray beam is uniform, if one is to obtain dot interlace scanning, it isnecessary? to modulate v.the electron'gun and to suppress or diminish the beam intensity during the time between the pas:- Is'agefrom' one point or elemental area to another. 'The'.resultni's that the average intensity of the light is very low and the light efficiency of the tubeis poor.

,l-According to theinvention, the new process overcomes these difficulties and permits the ,beamto remain on-each point an appreciable time. with an extremely rapid displacement of the spot during the transient time. As such transienttime may be'reduced to as low-as two per cent it follows that with the present invention the beam may be effective in providing image vproducing lighten the screen asmuch as ninety eightper cent. of; the time as compared with only twenty-five'per cent previouslyl The invention consists of combining a classical sawtooth generatorof large amplitude and of relatively low frequency as formerly utilized Application new 28, 1950; serial N6. 146,850

\ j.. 6 Claims. (01. ns-72, 6)

quency, low amplitude and of an opposite sign so as to hold the beam on an elemental areamst of the available time "and 'to produce: at. afprjedetermined sequential period of time (multiple of the low sawtooth frequency scanning), a very rapid deflection to the next elemental areat'ojbe explored. v i v I It is an object of the invention to obtam dot interlace scanning by means of two sawtooth generators having fractionally relatedfrequencies and connected to opposite deflectingplates or combined on one of the plates. v. H 7

If the deflection is made electromagnetically, the process consists in applying in the. same or in two parallel deflecting coils sawtooth currents of opposite signs and of frequencies which are widely different. In the case. of an electrostatic deviation, the normal sawtooth voltages are Tapplied to one plate and the complementary voltage of a high frequency sawtooth isfapplie'd to the other plate. The apparent discontinuous movement of the spot can be realized either horizontally and vertically or both ways. According to a particular improvement of'the inventionthe origin or beginning of the sawtooth 'of'high frequency can be shifted from that of. a lowffrequency sawtooth. The phase ,a shift can be changed at the beginning of the frame or 'at the beginning of the line. This process produces a dot'interlaced scanning; "According to the invention this dot interlaced process is usedjfor color television and particularly for the three color television system. The process "according to the invention permits spotting or holding of the beam as a function of time on the parts 'of the screen where elementary filters or dots of color phosphors are positioned so that the spot "appears to be of one color or of another. This color produced by filters or phosphors can'be disposed in the form of parallel colored bands or in form of a check pattern;

According to a particular improvement of the invention, the irregular movement of the' spot and the line interlace are combined with across motion of variable values of amplitude and phase shift'so that a knights move" type of scanning is obtained as disclosed in U. S. Patent 2,479,880. a The process and apparatus utilized in'theap- .plication ofthe invention will be betterunderstood from the following description which is to be taken as illustrative and not as limiting. In the drawings like numerals refer to likeiparts throughout. I

Figure l is a schematic general outline circuit for -practicing the invention.

time, the voltages in different parts of Fig. 1 and the resulting deflection of the beam spot.

Fig. 3 is a graph showing the voltages and deviations in the case of a variable phase shift between the origins of the high and the low frequency sawtooth waves according 'to'the invention.

Fig. 4 is a fragmentary diagrammatic showing of the screen scanning resulting fromthecombined deflections according to the invention.

Fig. 5 is a fragmentary diagrammatic showing of screen scanning in which phase-shiftis employed.

In Fig. 1 the usual video setI receives signals from a di-pole antenna or the like and is connected to a separator 2 which provides a video frequency at 4, a level line signal at v3.and an end image signal at I5. Line signal 3 is'supplied to the usual sawtooth generator 9 which it synchronizes with the transmitter. The output of sawtooth generator 9 is applied to deflection plate of cathode ray tube I3.

The end of image signal I5 is applied=to a second sawtooth generator I6 which is in-turn connected to deflection plate I4 of tube I3. Video frequency signal 4 is channeled to the grid I2 of the electron gun of C.-R. tube I3 and continuously modulates the intensity of the beam except where the signal is modulated to cut-off at the transmitter.

Line signal 3 is utilized to synchronize amultiplier 6. For example, if the number of lines of a frame is 819 and the number of elemental areas or points on each line is 900, the multiplication may be 300 for a three color system. As will be seen below the multiplication is preferably 300 plus a small proper fraction such as /2, /s, /4, r /s- Multiplier 6 is connected to a sawtooth generator 8 through a phase shift device such as delay line I. The output of multiplier 6 synchronizes generator 8. The output of generator 8 is applied to the second deflection plate II of tube I3. Generators 8 and 9 are mutually ad- .iusted to have voltages of the same value-and of the same polarity with respect to ground. They are also adjusted with respect to time. Under these conditions, the difference of potential between plates IIiand II is maintained unchangedduring the slow variation of the sawtooth of generator 8 and is abruptly modified at each line of relaxation of the higher frequency generator 9.

An illustration of voltage gradients is shown clearly in Fig. 2 which illustrates the voltage as a function of time for different parts of the Fig. 1.

I0 is the voltage applied to the plate III.

II is the voltage applied totheplate II.

The resulting difference of voltage and correspondingly the electrostatic field betweenplates I0 andI I is the diflerence between thetwocurves It is the step-by-stepcurVeiuf increasing value I8.

As a result of this arrangement, the fiyin'g'spot is maintained at the samelocation of'the screen during each voltage rise' III of the sawtooth generator 8 and moves very rapidly at the end of each sawtooth, from one location to the'other where it is again maintained for the same duration and so on across the screen.

According to an improvement of the invention. it is possible to change the sequence ofpoints of impact of the beam. This result is obtained in one form by the introduction of=retarding means of producing a phase-shift '1 onthe iine connect- 4 ing the multiplier 6 to the sawtooth generator or relaxator 8. The result of this delay line I is shown in the Fig. 3, which illustrates the voltage changes of deflection plates I 0 and II as a 'function of time.

If the *phase shift is the single step 19, the curve HR creates a voltage difference between plates I0 and II, with steps for values causing beam locations other than such as shown by G in which the phase shift is zero.

If the phase shift is 20, the curve HB creates another voltage differential with steps having another location and .so ion. In "the particular case where the phase shiftis zero for the curve HG, /3 of the sawtooth for the curve HR and of the sawtooth-for .IzIBitlis-possible to obtain a dot interlacedscanning of three points. This form of scanning is particularly valuable for a three color television process. In the present discussion R, B and G represent red, blue and green respectively. The combined results-of this action on plate ID in connection with actionon plate -I I appears on the screen asshown-in-Fig. 4. In this figure, the first scanning corresponds to the points IIG, the second-with.a -phase shift of 19 in Fig. "3 tothe shaded points HR, and the third with a phase shift of 20to-points I IB.

It is possible to control the phase shift so as to move the beam automatically without *using -a phase shift delay line 'L-if the end of line-signal 5 and the -multiplier --6 are not frequencies Which--are=multiples of one=another, buthave "a relation-which shifts-thebeam a fraction of a unit area-to which may be'added one-or-more whole unit area widths. :For example, if the frequency of multiplier-6-is-300 times the fre- 'dot'of thefollowing image-to'beshifted by one width with "respect to 'its "-previous location as shown in Fig. 4";where"I-IB-'and"I I'G are'in successive. images.

:A similar; result appears on 'the screen in' Fig-'5 for a "multiple of 300 plus one-half. The points explored'at the first line are shaded areasfz I ,1 2 I. at the second .22, '22,"at 'the third "23, "23 these points'arenotone' under'the other but are shifted oneandone half pointsgbetweenithe other.

i If thexnumber of lines of the" image isv a" multiple of ;three"to, WhiOh.iS added one unit, the points scanned are shifted automatically from the Ipreceding E'frame at the'end of exploration of the image 'and'the points explored" in" the 'following image are'the'crossed areas 24, 2 4for the first line, 25, 25 for the second line and so on 26;and 26 etc. "At the.'foll0wing scanning-of the factor of 300' plusa-ny small properfraction-such as-' A, and so on. "Thexuse of'% may in- "troduce a colorline in a three -color system. Accordingly /2 or -are -preferred in such a system. Thesmaller fractions lengthen the cycle of =recurrence and increase'the number of ele- -mental areas' in a group.

In the u preceding embodiments of the inventiomtthe linesmre-tscanneddnssuccessicn. ".iThe

same process may be used in a system of interlaced line scanning to great advantage with the apparent result of skip location such as obtained in th knights move as disclosed in the above cited application.

For color television, employing dot interlace, this process allows for control of color flicker, color cross talk, and yields a better blending result.

I claim:

1. In an electron beam scanning system, an explored surface defined by a plurality of groups of elemental areas, means for generating an electron scanning beam, means for deflectin said beam, means connected to said deflecting means for holding said beam on an elemental area, said holding means and said deflecting means being so timed that at least one elemental area in each of said groups is scanned during each scanning of said surface and that different elemental areas in each of said groups are scanned during successive scannings of said surface and the beam is held on each elemental area for a period longer than the time expended in deflecting the beam from one elemental area to another and phase shift means connected toshift periodically the local position of the beam by a partial step whereby the space between adjacent dots remains the same, but the position of the dots is shifted slightly to yield dot interlace scanning.

2. In combination, a television receiver comprising a video unit, a separator unit connected thereto, a cathode ray tube, connected to said separator unit, two wave generators connected to the beam deflection means of said tube, one of said generators producing a wave of relatively low frequency and the other generator producing a wave of relatively high frequency and phase shift means connected to one of said generators to shift periodically the relation between the high and low frequencies whereby the electron beam of said tube is held momentarily on an elemental area of the face of said tube, periodically jumps with high speed to other elemental areas and periodically shifts position by partial steps with the space between adjacent dots for selected sequences remaining the same to yield dot interlace scanning.

3. The combination set forth in claim 2, said phase shift means connected to the generator producing the relatively high frequency whereby the space relation of the high and low frequencies is changed by a partial step at the beginning of each of a series of sequences and dot interlaced scanning of three points is obtained.

4. The combination set forth in claim 3, multiplier means connected to said high frequency generator and having a, multiplication factor of at least one hundred plus a proper fraction.

5. In a three color television system, a cathode ray tube having beam deflection means, two wave generators connected to said beam deflection means, said generators producing low and high frequency waves with respect to each other, the frequency of said high frequency generator being a mixed number and means connected to one of said generators to change periodically the phase relation of said waves by a partial step at the beginning of each of a series of selected sequences whereby successive sequences begin with a different color.

6. The combination set forth in claim 5, the

' fractional part of said mixed number being other than one third.

PIERRE MARIE GABRIEL TOULON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,143,933 Barthelemy Jan. 17, 1939 2,250,819 Wolf July 29, 1941 2,328,248 Andrieu Aug. 31, 1943 2,368,448 Cook Jan. 30, 1945 2,385,563 Beers Sept. 25, 1945 2,402,270 Altman June 18, 1946 2,406,382 Kellogg Aug. 2'7, 1946 2,414,939 Fitch Jan. 28, 1947 2,426,201 Grieg Aug. 26, 1947 2,439,324 Walker Apr. 6, 1948 2,465,355 Cook Mar. 29, 1949 2,474,266 Lyons June 28, 1949 2,479,880 Toulon Aug. 23, 1949 2,501,857 Stewart Mar. 28, 1950 

